1. Field of the Invention
The present invention generally relates to a so-called scanning fluorescent X-ray analyzer and, more particularly, to a path switching device used in association with the scanning fluorescent X-ray analyzer for selecting one of three or more optical detection paths along which respective beams to be analyzer travel.
2. Description of the Prior Art
Hitherto, the fluorescent X-ray analyzer of a so-called wavelength divergence type is, as shown in FIG. 4, so designed as to irradiate a sample piece 1 with a primary X-ray 3, generated from an X-ray source 4 such as, for example, an X-ray tube, to cause the sample piece 1 to generate a fluorescent X-ray (secondary X-ray) 5 which is, after having been passed through a divergent slit 13, subsequently monochromatized by a monochromator 6 to provide a monochromatized fluorescent X-ray 7 that is finally detected by a detector 8. In this type of the fluorescent X-ray analyzer, the detector 8 makes use of two counters, i.e., a gas-flow proportional counter tube (hereinafter referred to as "F-PC") 8A for detection of the low-energy fluorescent X-rays and a scintillation counter (hereinafter referred to as "SC") 8B for detection of the high-energy fluorescent X-rays. A light receiving slit 11A is disposed in front of the SC 8B, whereas the F-PC 8A has a light receiving slit (not shown) built therein at a front thereof.
According to the prior art, when the high-energy fluorescent X-ray 7 is desired to be measured, in order to vary the wavelength of the fluorescent X-ray 7 incident upon the SC 8B, the use has been made of a linkage means (not shown) for continuously associating the monochromator 6 with both of the light receiving slit 11A and the SC 8B so that fluorescent X-rays 5 generated from various elements contained in the sample piece 1 can be monochromatized according to respective wavelengths with the intensity thereof subsequently measured.
In other words, when the fluorescent X-ray 5 impinges upon the monochromator 6 at an angle of incidence .theta., an extension 9 of the path of travel of the fluorescent X-ray 5 having passed through the divergent slit 13 and the fluorescent X-ray 7 that has been monochromatized by the monochromator 6 form an angle of diffraction 2.theta. which is twice the angle of incidence .theta.. However, the linkage means referred to above serves to vary the angle of diffraction 2.theta. to vary the wavelength of the monochromatized fluorescent X-ray 7 so that the monochromatized fluorescent X-ray 7 can enter the SC 8B through the light receiving slit 11A. In other words, the linkage means is operable to rotate the monochromator 6 about a pivot axis O lying perpendicular to the plane of a sheet of the drawing of FIG. 4 and passing across the center of a light receiving surface of the monochromator 6, and also to turn, in synchronism with rotation of the monochromator 6, both of the light receiving slit 11A and the SC 8B about the pivot axis O along a circular path 12A through an angle that is equal to twice the angle of rotation of the monochromator 6.
More specifically, a .theta. spindle (not shown) having the monochromator 6 mounted thereon with the pivot axis O passing through the light receiving surface of the monochromator 6 and coaxially occupied by the .theta. spindle is rotated to cause a 2.theta. spindle (not shown), on which the F-PC 8A and both of the light receiving slit 11A and the SC 8B are mounted in side-by-side relation in a direction conforming to the direction of turn thereof, to be turned an angle equal to twice the angle of rotation of the .theta. spindle.
On the other hand, where the intensity of the low-energy fluorescent X-ray 7 is desired to be measured, the angle at which the monochromator 6 is fitted to the .theta. spindle is turned to a predetermined angle so that the fluorescent X-ray 7 monochromatized by the monochromator 6 can enter the F-PC 8A. (This also applies where the analyzer includes a plurality of monochromators and one of the monochromators is selectively utilized.) The linkage means operates in a manner similar to that described above.
Thus, in this prior art fluorescent X-ray analyzer, a detection path extending from the monochromator 6 to the SC 8B via the light receiving slit 11A and a detection path extending from the monochromator 6 to the F-PC 8A can be selectively utilized one at a time.
With the prior art fluorescent X-ray analyzer, it has been found that since the SC 8B is fixed in position at a location rearwardly of the light receiving slit 11A and mounted on the 2.theta. spindle, it is impossible to position the SC 8B at a location rearwardly of the F-PC 8A. Accordingly, a third detection path can in no way be selected, which would be necessitated where even though the fluorescent X-ray 7 has been received by the F-PC 8A, a portion of the fluorescent X-ray 7 having passed beyond the F-PC 8A without being measured as to its intensity completely is to be measured by the SC 8B so that the intensity of the fluorescent X-ray 7 as a whole can be accurately measured by summing the intensity of the fluorescent X-ray 7 measured by the F-PC 8A and the intensity of the remaining portion of the fluorescent X-ray 7 measured by the SC 8B together.